Graduate Program in Molecular Plant Sciences, Washington State University, Pullman, WA, 99164-1030, USA; Department of Horticulture, Washington State University, Pullman, WA, 99164-6414, USA.
Plant J. 2014 Apr;78(2):269-81. doi: 10.1111/tpj.12473. Epub 2014 Mar 26.
Transient changes in intracellular Ca(2+) concentration are essential signals for activation of plant immunity. It has also been reported that Ca(2+) signals suppress salicylic acid-mediated plant defense through AtSR1/CAMTA3, a member of the Ca(2+) /calmodulin-regulated transcription factor family that is conserved in multicellular eukaryotes. How plants overcome this negative regulation to mount an effective defense response during a stage of intracellular Ca(2+) surge is unclear. Here we report the identification and functional characterization of an important component of ubiquitin ligase, and the associated AtSR1 turnover. The AtSR1 interaction protein 1 (SR1IP1) was identified by CytoTrap two-hybrid screening. The loss-of-function mutant of SR1IP1 is more susceptible to bacterial pathogens, and over-expression of SR1IP1 confers enhanced resistance, indicating that SR1IP1 acts as a positive regulator of plant defense. SR1IP1 and AtSR1 act in the same signaling pathway to regulate plant immunity. SR1IP1 contains the structural features of a substrate adaptor in cullin 3-based E3 ubiquitin ligase, and was shown to serve as a substrate adaptor that recruits AtSR1 for ubiquitination and degradation when plants are challenged with pathogens. Hence, SR1IP1 positively regulates plant immunity by removing the defense suppressor AtSR1. These findings provide a mechanistic insight into how Ca(2+) -mediated actions are coordinated to achieve effective plant immunity.
细胞内钙离子浓度的瞬时变化是植物免疫激活的重要信号。据报道，钙离子信号通过 AtSR1/CAMTA3 抑制水杨酸介导的植物防御，AtSR1/CAMTA3 是钙/钙调素调节转录因子家族的成员，在多细胞真核生物中保守。在细胞内钙离子激增的阶段，植物如何克服这种负调控，从而产生有效的防御反应，目前尚不清楚。在这里，我们报告了泛素连接酶的一个重要组成部分及其相关的 AtSR1 周转率的鉴定和功能特征。AtSR1 相互作用蛋白 1（SR1IP1）是通过 CytoTrap 双杂交筛选鉴定的。SR1IP1 的功能丧失突变体对细菌病原体更敏感，而 SR1IP1 的过表达赋予了增强的抗性，表明 SR1IP1 作为植物防御的正调节剂发挥作用。SR1IP1 和 AtSR1 在同一信号通路中作用，以调节植物免疫。SR1IP1 含有基于 cullin 3 的 E3 泛素连接酶中底物衔接子的结构特征，并且当植物受到病原体挑战时，它被证明作为一种底物衔接子，招募 AtSR1 进行泛素化和降解。因此，SR1IP1 通过去除防御抑制剂 AtSR1 来正向调节植物免疫。这些发现为钙离子介导的作用如何协调以实现有效的植物免疫提供了机制上的见解。
